Patients having a heart condition known as ventricular dilatation are in a clinically dangerous condition when the patients are in an end stage cardiac failure pattern. The ventricular dilatation increases the load on the heart (that is, it increases the oxygen consumption by the heart), while at the same time decreasing cardiac efficiency. A significant fraction of patients in congestive heart failure, including those who are not in immediate danger of death, lead very limited lives. This dilatation condition does not respond to current pharmacological treatment. A small amount, typically less than 10%, of the energy and oxygen consumed by the heart, is used to do mechanical work. Thus the balance, which is the major part of the energy consumed by the heart is used in maintaining the elastic tension of the heart muscles for a period of time. With a given pressure, the elastic tension is directly proportional to the radius of curvature of the heart ventricle. During ventricular dilatation the ventricular radius increases and the energy dissipated by the heart muscle just to maintain this elastic tension during diastole is abnormally increased, thereby increasing oxygen consumption. A number of methods and devices have been employed to aid the pumping action of failing hearts. Many of these include sacs or wraps placed around the failing heart, or, in some instances only around the ventricle of the failing heart, with these wraps constructed to provide for active pumping usually, but not always, in synchronism with the ventricular pumping of the natural heart. Table 1 lists a number of developed devices with pertinent operating characteristics.
TABLE 1 Pul- Blood sa- Con- Level of til- tact- Device Support ity Duration ing Comments IABP Partial &lt;20% Y Days to Y Counter- Months pulsation provides LV unloading Biopump Full N Days Y Limited to short duration due to thrombotic potential Thoractec Full Y Months Y Sac-type actuation Novacor Full Y Months Y Sac-type pump with electric actuation Hemopump Partial N Days Y Axial flow 50-75% pump Heart Mate Full Y Months Y Pusher-Plate pneumatic and electric Aortic Patch Partial Y Months Y Counter- pulsation BVS 5000 Full Y Weeks Y Designed for temporary support Anstadt Full Y Days N Cardiac resuscitation Cardio- Partial Y Years N Requires myoplasty &lt;20% muscle training
One, more recent development involves the wrapping and pacing of a skeletal muscle around the heart to aid in the pumping. In that configuration, a pacemaker is implanted to control the timing of the activation of the wrapped around skeletal muscle.
It is an object of this invention to provide a completely passive girdle to be wrapped around a heart suffering from ventricular dilatation to limit this dilatation and thus improve the performance characteristics of the heart.
It is another object of this invention to provide a passive girdle or vest which can, over a period of time, have its diameter decreased to effect some decrease in dilatation of the ventricle.
Other objects will become apparent in accordance with the description of the preferred embodiments below.